Hatching dates of waders and mowing dates in intensively exploited grassland areas in different years Original Research Article

Intensification of grassland management threatens grassland breeding waders such as lapwing Vanellus vanellus, black-tailed godwit Limosa limosa and redshank Tringa totanus in several European countries. Temperature sums (a measure of spring warming) are shown to be associated with hatching dates of two of the three studied species and with mowing. Because birds nested earlier in years with early mowing, the negative effect of mowing on hatching success was limited. This is contrary to the general idea among conservationists that grassland breeding birds have a more or less fixed breeding season and that early mowing will therefore reduce their breeding success severely. By postponing the current median mowing dates by 1–2 weeks, the probability of the clutches surviving mowing may be increased to the level necessary for maintaining the current population levels. Farmers could contribute to the conservation of these waders by using these well-known temperature sums for predicting hatching dates.